Field of the Invention
This invention relates to improvements in tool cutting path generation. More particularly, the proposed tool path program reduces the machining time while the cutter is finishing the walls by removing the finishing-stock at the higher speeds and maintaining such high cutting velocity/feed-rate in the corners by removing the excess material in 3 or 4 successive cuts depending upon the volume to be removed before continuing to finish along the walls and entering into other corners throughout its trajectory.
Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Many parts are machined from a blank of solid material or are finish machined from a casting to achieve the desired end dimensions. For these types of applications the cost to produce the finished part is significantly affected by the amount of time it takes to machine the part. In addition, cutting the part at a rapid speed also affects the quality of the finish on the surface of the part. Multiple fine passes can cause a smooth end result, but at a compromise of the cost to produce the finished part. At the other extreme, quickly cutting the part can result in an unacceptable rough part where the part can have surface imperfections and be prone to early failure.
One of the most critical parts to machine is corners where there is limited clearance for chips to be removed from the corner as the end mill provides a roughing and/or a finishing operation. When the machining is repeatedly performed on multiple parts a time savings of seconds, minutes, hours or more to machine a part has significant impact on the cost of the finished part and the potential profit. Most prior art patents simply generate a cutting tool path to provide a finished part by removing 2-D layers or by making multiple cuts as the tool closes-in to the final dimension. Time spent where the cutter is being re-positioned further reduces efficiency because no material removal is being performed. Keeping the cutter moving at a consistent speed is not optimal and the feed rate should be adjusted based upon the depth of the cut and the amount of material being removed.
For finishing walls of any given multi sided pocket, traditional offset would yield cutter overload in the corners of tool motion. Currently there are a few choices being used in industry to overcome this problem by such as picking corners and then go for finish. This increases amount of time in machining and programming since each tool motion has to be done separately. A number of patents and or publications have been made to address these issues. Exemplary examples of patents and or publication that try to address this/these problem(s) are identified and discussed below.
U.S. Pat. No. 4,970,164 issued Mar. 6, 1990 to Margaret K. Guyder discloses an Automatically Optimized NC Tool Path Generation for Machining. This method is presented to generate 2D tool paths and to optimize the ordering of these tool paths for 2½ axis milling of cavities for molds and dies. The optimization is for the generation of the tool path in a 2-D environment and does not optimize the tool for speed or efficiency nor does it account for sensitive milling of corner.
U.S. Pat. No. 7,451,013 issued Nov. 11, 2008 to Glenn Coleman et al discloses Engagement Milling. The method includes the steps of storing a maximum engagement of the milling cutter and defining each one of the one or more passes such that a value of the engagement, when traversing each one of the one or more passes, does not exceed the maximum value of engagement. While this method provides multiple passes through an area where material is being removed the method does not optimize for the tool passing over the same area multiple times as the tool returns to remove more material on subsequent passes. This method only targets roughing strategy and does not address any finishing strategy. Moreover, it produces higher amount of non-cutting moves.
U.S. Pat. No. 7,930,054 issued Apr. 19, 2011 to Slaughter et al discloses a Method and System for Tool path Generation. The method includes exporting CAD defined 3-D geometry to a slicing module; slicing the 3-D geometry creating a set of 2-D patterns representing the 3-D geometry; generating vector code from the set of 2-D patterns; and translating the vector code to machine code. While the tool path is generated from 3-D geometry to a 2-D pattern there is no efficiency made to reduce the total machining time.
What is needed is a method where the cutter will finish the walls and when approaching the corners then it will maintain the proper load on the cutter by gradually decreasing the distance to be machined the corners. And user can control the distance in corners by a maximum defined volume to be cut. The disclosure found in this document provides a solution to this problem.